Cross-linked (bisphenol-S, formaldehyde, 1,6-hexadiamine) terpolymer for the adsorption of Pb2+ ions from aqueous solutions

ABSTRACT

A cross-linked terpolymer (BSDF) obtained by polycondensation of bisphenol-S, formaldehyde and 1,6-diaminohexane. The terpolymer is highly efficient in eliminating lead ions from aqueous solutions. The adsorption of lead ions on BSDF was studied under different conditions such as: pH, contact time and temperature. The adsorption kinetics fits Lagergren second order kinetic model that are in agreement with the low surface area as a chemisorption process. Applying BSDF on non-spiked and spiked real wastewater samples under optimum conditions revealed the high efficiency of BSDF in removing toxic metal ions.

BACKGROUND OF THE INVENTION

Technical Field

The present invention relates to a cross-linked terpolymer, a method ofmaking the terpolymer, and a method of removing lead ions from anaqueous solution wherein the terpolymer adsorbs the lead ions from theaqueous solution.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Sustainable water supplies are vital for human consumption, agriculturerequirements and industry supplies. Wastewaters have always been aproblem due to their increasing toxic threat to humans and theenvironment. Because of the development in technology and the increasein industrial activity, pollutants released into the environment havebeen increasing continuously. Due to their toxicity, there is asignificant threat to the environment and public health (H. L. Ge, S.Liu, B. X. Su, L. T. g Qin, Predicting synergistic toxicity of heavymetals and ionic liquids on photobacterium Q67, J. Hazard. Mater., 268(2014) 77-83; M. Ove

ka, T. Taká

, Managing heavy metal toxicity stress in plants: Biological andbiotechnological tools, Biotechnology Advances, 32, 1 (2014) 73-86—eachincorporated herein by reference in its entirety).

Even at low levels, lead as heavy metal is toxic, non-biodegradable andtends to bio-accumulate in cells of living systems (M. Javed, M. A.Saeed, Growth and bioaccumulation of iron in the body organs of Catlacatla, Labeo rohita and Cirrhina mrigala during chronic exposures,International Journal of Agriculture and Biology 12, 6 (2010)881-886—incorporated herein by reference in its entirety). Leadpoisoning in humans, especially in children six years old and undercauses severe damage to organs like the kidney, nervous system,reproductive system, liver and brain (C. F. Bearer, Environmental healthhazards: how children are different from adults, The future of childrencritical issues for children and youths, 5, 2 (1995) 11-26—incorporatedherein by reference in its entirety). The primary sources of leadexposure for humans is lead-based paint in old-homes and lead indrinking water (H. W. Mielke and P. L. Reagan, Soil is an importantpathway of human lead exposure, Environ health perspect. 106 (1998)217-229; M. D. Sanborn, A. Abelsohn, M. Campbell, E. Weir, CMAJ 166, 10(2002) 1287-1292—each incorporated herein by reference in its entirety).

As per the World Health Organization (WHO) standard, the maximum levelof lead in drinking water is 0.01 mg/l, and as per the Drinking WaterStandards and Health Advisories 2012 Edition, US EnvironmentalProtection Agency, the maximum contaminant level goal of lead fordrinking water is zero (WHO, Guidelines for Drinking-Water Quality, 3rded., World Health Organization, Geneva, Switzerland, 2006; DrinkingWater Standards and Health Advisories, EPA 822-S-12-001, Office of WaterU.S. Environmental Protection Agency Washington, D.C., 2012 Edition,U.S. Environmental Agency, Drinking Water Cont.,http://www.epa.gov/safewater/contaminants/index.html—each incorporatedherein by reference in its entirety). However, effluents discharged fromvarious industries usually contain lead in an amount above this level.To achieve this goal, various technologies have been developed to removelead from wastewaters. This includes precipitation, coagulation, reverseosmosis, ion exchange, solvent extraction, flotation, and membraneseparation. However, among the various techniques, adsorption isconsidered the most efficient method for the treatment and eliminationof lead in wastewater. This is because of its simple design and itsmerits of effectiveness, efficiency and free sludge (F. Rozada, M.Otero, A. Moran, A. I. Garcia. Adsorption of heavy metals onto sewagesludge-derived materials. Bioresource Technology 99 (2009) 6332-6338;Dabrowski, A. Adsorption, from theory to practice. Adv. Colloid Int.Sci. 93 (2001) 135-224; A. Celik, A. Demirbas, Removal of heavy metalions from aqueous solutions via adsorption onto modified lignin frompulping wastes. Energy Sources 27 (2005) 1167-1177—each incorporatedherein by reference in its entirety). Several materials have beeninvestigated for the adsorption of lead (S. J. T. Pollard, G. D. Fowler,C. J. Sollars, and Perry, R. Low-cost adsorbents for waste andwastewater treatment: A review. Sci. Total Environ., 116 (1992) 31-37;S. E. Bailey, T. J. Olin, R. M. Bricka, and D. D. Adrian, A review ofpotentially low-cost sorbents for heavy metals. Water Res. 33 (1999)2469-2473; S. Babel, and T. A. Kurniawan, Low-cost adsorbents for heavymetals uptake from contaminated water: A review. J. Hazard. Mater. 97(2003) 219-225; S. S. Ahluwalia, and D. Goyal, Microbial and plantderived biomass for removal of heavy metals from wastewater. Bioresour.Technol. 98 (2007) 2243-2257; M. E. Russo, F. Di Natale, V. Prigione, V.Tigini, A. Marzocchella, G. C. Varese, Adsorption of acid dyes on fungalbiomass: equilibrium and kinetics characterization. J. Chem. Eng. 162(2010) 537-545; K. K. Singh, M. Talat, S. H. Hasan, Removal of lead fromaqueous solutions by agricultural waste maize bran. Bioresour. Technol.97 (2006) 2124-2130—each incorporated herein by reference in itsentirety). Promising classes of polymeric adsorbents like cross-linkedpolymers that contain some carboxyl motifs (E. H. Rifi, F. Rastegar, J.P. Brunette, Uptake of cesium, strontium and europium by a poly(sodiumacrylate-acrylic acid) hydrogel, Talanta 42 (1995) 811-816; C. Ozeroglu,G. Keceli, Removal of strontium ions by a crosslinked copolymercontaining methacrylic acid functional groups, J. Radioanal. Nucl. Chem.268 (2006) 211-219—each incorporated herein by reference in itsentirety) like derivatives based on carboxylated polysaccharides (M.Wang, L. Xua, J. Peng, M. Zhai, Adsorption and desorption of Sr(II) ionsin the gels based on polysaccharide derivates, J. Li, G. Wei, J. Hazard.Mater. 171 (2009) 820-826—incorporated herein by reference in itsentirety) were also found to adsorb heavy metal ions. Chelating agentscontaining an aminomethylphosphonate moiety were tested and found tohave attractive properties as exchange resins with ligands for selectivemetal ion complexation or phosphonic acid groups to extract heavy metalions from aqueous solutions or from fuel ethanol solutions (K. P.Ripperger, S. D. Alexandratos, Polymer-supported phosphorus-containingligands for selective metal ion complexation. In Studies in SurfaceScience and Catalysis; Dabrowski, A., Ed.; Elsevier Science B.V.:Amsterdam, The Netherlands, 120 (1998) 473-495; K. Yamabe, T. Ihara, A.Jyo, Metal ion selectivity of macroreticular chelating cation exchangeresins with phophonic acid groups attached to phenyl groups ofstyrene-divinylbenzene copolymer matrix. Sep. Sci. Technol. 36 (2001)3511-3528; D. Ko

odyńska, Z. Hubicki, M. Geüca, Application of a new generationcomplexing agent in removal of heavy metal ions from aqueous solutions.Ind. Eng. Chem. Res. 47 (2008) 3192-3199; Z. Wang, P. Yin, R. Qu, Q. Xu,Heterogeneous synthesis of chelating resin organophosphonicacid-functionalized silica gel and its adsorption property of heavymetal ions from fuel ethanol solutions. J. App. Polym. Sci. 126 (2012)544-551—each incorporated herein by reference in its entirety).Diethylenetriamine-functionalized polymeric adsorbents, prepared byamination of micro-beads synthesized from glycidyl methacrylate andtrimethylolpropane trimethacrylate co-polymerization, have been reportedfor selective removal of copper and lead ions (C. Liu, R. Bai, Q. S. Ly,Selective removal of copper and lead ions bydiethylenetriamine-functionalized adsorbent: Behaviors and mechanisms,Water Res. 42 (2008) 1511-1522—incorporated herein by reference in itsentirety). Amino/polycarboxylic acid functionalized polymeric adsorbentshave been reported to have good chelating properties toward heavy metalions and thus can be used for the treatment of waste water (E. Repo, J.K. Warchol, A. Bhatnagar, A. Mudhoo, M. Sillanpa, Aminopolycarboxylicacid functionalized adsorbents for heavy metals removal from water,Water Res. 47 (2013) 4812-4832; K. Inoue, K. Ohto, K. Yoshizuka, T.Yamaguchi, T. Tanaka, Adsorption of lead(II) ion on complexane types ofchemically modified chitosan. Bull. Chem. Soc. Jpn. 70 (1997) 2443-2447;X. F. Liang, W. G. Hou, Y. M. Xu, G. H. Sun, L. Wang, Y. Sun, X. Qin,Sorption of lead ion by layered double hydroxide intercalated withdiethylenetriaminepentaacetic acid. Colloid Surf. A 366 (2010) 50-57; L.Yang, Y. Li, X. Jin, Z. Ye, X. Ma, L. Wang, Y. Liu, Synthesis andcharacterization of a series of chelating resins containingamino/imino-carboxyl groups and their adsorption behavior for lead inaqueous phase. Chem. Eng. J. 168 (2011) 115-124; O. Karniz Junior, L. V.A. Gurgel, R. P. Freitas, L. F. Gil, Adsorption of Cu(II), Cd(II), andPb(II) from aqueous single metal solutions by mercerized cellulose andmercerized sugarcane bagasse chemically modified with EDTA dianhydride(EDTAD). Carbohydr. Polym. 77 (2009) 643-650; L. Wang, L. Yang, Y. Li,Y. Zhang, X. Ma, Z. Ye, Study on adsorption mechanism of Pb(II) andCu(II) in aqueous solution using PS-EDTA resin. Chem. Eng. J. 163 (2010)364-372—each incorporated herein by reference in its entirety). Suchmaterials have been also reported for their regenerability andrecycling, which is a crucial step in increasing the practicalapplicability of the adsorbent (J. Huang, M. Ye, Y. Qu, L. Chu, R. Chen,Q. He, D. Xu, Pb(II) removal from aqueous media by EDTA—modifiedmesoporous silica SBA-15. J. Colloid Interface Sci. 385 (2012)137-146—incorporated herein by reference in its entirety).

BRIEF SUMMARY OF THE INVENTION

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

One embodiment of the disclosure describes a cross-linked terpolymer.

In another embodiment the cross-linked terpolymer comprisespolycondensed units of bisphenol-S, 1,6-diaminohexane, and formaldehyde.

In another embodiment the diamino unit of 1,6-diaminohexane bridges thearyl groups of the bisphenol unit through a nitrogen-carbon-aryllinkage.

In another embodiment the bisphenol-S, 1,6-diaminohexane, andformaldehyde units of the cross-linked terpolymer are present in a molarratio of 1:2:4, respectively.

In another embodiment the terpolymer is in the form of a solid having asurface area in the range of 0.720-0.750 m² g⁻¹.

In another embodiment the terpolymer is in the form of a solid having apore size diameter in the range of 161.0-163.0 nm.

In another embodiment the terpolymer is in the form of a solid having atotal pore volume in the range of 0.028-0.032 cm³ g⁻¹.

In another embodiment terpolymer is an adsorbent in the removal of leadions from an aqueous solution.

In another embodiment the terpolymer effectively removes at least 90% ofthe lead ions from the aqueous solution.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a TGA analysis of a terpolymer (BSDF);

FIG. 2 is an FT-IR spectra for BSDF and BSDF loaded with lead ions;

FIG. 3 is a graph that shows the effect of pH on the adsorption capacityof Pb²⁺ ions by BSDF;

FIG. 4 is a graph that shows the percent removal of Pb²⁺ ions by BSDF atdifferent temperatures;

FIG. 5A shows the effect of time on the adsorption of Pb²⁺ by BSDF atdifferent temperatures,

FIG. 5B shows the Lagergren-second order kinetics of Pb²⁺ adsorption onBSDF at different temperatures,

FIG. 5C shows the activation energy determination for Pb²⁺ adsorption onBSDF,

FIG. 5D shows an intraparticle diffusion plot for Pb²⁺ adsorption onBSDF at different temperatures;

FIG. 6A shows SEM images and EDX analyses for BSDF; and

FIG. 6B shows SEM images and EDX analyses for BSDF loaded with leadions.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views.

One embodiment of the disclosure relates to a cross-linked terpolymer.The cross-linked terpolymer has a formula I:

The number of repeating units of the polymer is represented by “n” whichmay be an integer of from greater than 1 to 10,000 1, preferably from 10to 5,000, 20 to 2,500, 25 to 1,500, or 100 to 1,000. There are two alkylunits that link the pair of amino groups of the terpolymer (derived froma C₆ diamino group). The alkyl bridges are bonded to a bis-phenol groupthrough a single carbon atom (e.g., derived from formaldehyde). Thealkyl unit connects the two amino groups to one another. The alkyl unitmay be substituted or unsubstituted. In one embodiment alkyl unit is asix carbon chain that is substituted with one or more alkyl groupsselected from the group consisting of methyl, ethyl, propyl, butyl,pentyl, hexyl any isomers thereof, a C₁-C₆ alkoxy group, an aryl groupand/or a halogen atom. The alkyl unit represents a diaminohexane groupwhich bridges the phenol groups of the terpolymer.

Each amino group is further bonded to an aryl group of a phenolic unit.Two phenol functional groups of a repeating unit are bonded to oneanother through a sulfonyl group The phenols groups are a part of abisphenol moiety that may be substituted or unsubstituted. The arylgroups of the bisphenol may likewise optionally be substituted with oneor more alkyl groups selected from the group consisting of methyl,ethyl, propyl, butyl, pentyl, hexyl any isomers thereof, a C₁-C₆ alkoxygroup, an aryl group and/or a halogen atom.

In other embodiments the bisphenol moiety is selected from the groupconsisting of 2,2-bis(4-hydroxyphenyl)propane,1,1-bis(4-hydroxyphenyl)-1-phenyl-ethane,2,2-bis(4-hydroxyphenyl)hexafluoropropane,2,2-bis(4-hydroxyphenyl)butane, bis-(4-hydroxyphenyl)diphenylmethane,2,2-bis(3-methyl-4-hydroxyphenyl)propane,bis(4-hydroxyphenyl)-2,2-dichlorethylene,1,1-bis(4-hydroxyphenyl)ethane, bis(4-hydroxydiphenyl)methane,2,2-bis(4-hydroxy-3-isopropyl-phenyl)propane,1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene,5,5′-(1-methylethyliden)-bis[1,1′-(bisphenyl)-2-ol]propane,1,1-bis(4-hydroyphenyl)-3,3,5-trimethyl-cyclohexane, and1,1-bis(4-hydroxyphenyl)-cyclohexane. Preferably the bisphenol compoundis the bis(4-hydroxyphenyl)sulfone shown in formula (I). Preferably thecross-linked terpolymer comprises polycondensed units of bisphenol-S,1,6-diaminohexane, and formaldehyde (i.e., BSDF).

In another embodiment one or more metal ions are coordinated to one ormore nitrogen atoms of the polymer. The metal ions that are coordinatedto the are preferably heavy metal ions have a 2+ charge including Pb²⁺,Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Cd²⁺ but may include Be²⁺ and/or Zn²⁺.

In another embodiment the weight average molecular weight of theterpolymer is in the range of including but not limited to 1,500-350,000g/mol, 2,500-300,000 g/mol, 3,000-100,000 g/mol, or 5,000-50,000 g/mol.

In another embodiment the terpolymer is in the form of a solid materialhaving a surface area in the range of 0.70-0.750 m² g⁻¹, preferably0.720-0.750 m² g⁻¹, or about 0.730 m² g⁻¹. In another embodiment theterpolymer is in the form of a solid material having a pore sizediameter in the range of 50-500 nm, preferably 75-450 nm, 100-400 nm,125-350 nm, 150-300 nm, 175-200 nm, especially preferably 161.0-163.0nm. In another embodiment the terpolymer is in the form of a solidmaterial having a total pore volume in the range of 0.020-0.04 cm³ g⁻¹,preferably 0.025-0.035 cm³ g⁻¹, 0.027-0.031 cm³ g⁻¹, 0.028-0.032 cm³g⁻¹. In another embodiment terpolymer is an adsorbent in the removal oflead ions from an aqueous solution.

EXAMPLES

Elemental analysis was performed by a Perkin Elmer elemental analyzerSeries 11 Model 2400. Infrared spectra were determined on a Perkin Elmer16F PC FTIR spectrometer. Concentrations of lead ions before and afteradsorption were determined using Thermo Scientific iCE 3000 flame atomicabsorption spectrometer (FAAS) equipped with a 10 cm air-acetyleneburner. Concentration of metal ions in Real waste-water samples weredetermined using inductively coupled plasma mass spectrometry (ICP-MS)model ICP-MS XSERIES-II Thermo Scientific (Table 1). Table 1 ispresented below.

TABLE 1 Instrument parameters for ICP Model ICP-MS XSERIES-II ThermoScientific RF power 1404 W Plasma gas flow 13 (L/min) Nebulizer gas flow0.95 (L/min) Auxiliary gas flow 0.7 (L/min) Nebulizer Quartz pneumaticnebulizer Spray chamber Glass with peltier cooling Number of replicates 3 Acquisition mode Pulse counting Dwell time 10 (ms) Sweeps/reading 100Acquisition parameters Scanning mode Peak Hopping Dwell time 300 msIntegration mode Peak area

Micrometrics ASAP 2020 BET surface area analyzer withBurnauer-Emmett-Teller (BET) N₂ method was employed to determine thesurface area of BSDF. Both Brunauer-Emmett-Teller (BET) method and thepore volumes were taken at the P/P₀=0.974 single point. Pore sizediameter was recorded by the Barrett-Joyner-Halenda method (BJH).Scanning electron microscope, TESCAN MIRA 3 (Czech Republic) equippedwith Oxford, was employed to determine the morphology of the polymersamples before and after the adsorption process. The elemental analysisof the samples was also conducted by Energy-dispersive X-rayspectroscope (EDX) equipped with a detector model X-Max. Also, theThermogravimetric analysis of the synthesized BSDF was conducted by athermal analyzer (STA 429) (Netzsch-Germany) at a constant heating rateof 10° C./min under nitrogen flow.

Bisphenol-S(4,4′-sulfonyldiphenol), 1,6-diaminohexane, paraformaldehydeand dimethylformamide were purchased from fluka Chemie AG (Buchs,Switzerland) and used as received without purification. Solvents andother chemicals used were of analytical grade.

Synthesis of Terpolymer (BSDF)

A mixture of bisphenol-S (0.01 mol, 2.50 g), 1,6-diaminohexane (0.02mol, 2.32 g) and paraformaldehyde (0.06 mol, 1.50 g) indimethylformamide (25 ml) was stirred at 80° C. for 24 h. once thetemperature reached 60° C., within 3 minutes a yellow resinous materialformed which was allowed to cure for 24 hours, the resinous material waswashed with water and ethanol several times in order to remove anyunreacted material and dried under vacuum at 60° C. until constantweight was achieved (4.98 g, 83%) (Scheme 1). (Found: C, 63.1; H, 8.5;N, 10.5; S, 5.9%. requires: C, 63.1; H, 8.3; N, 10.5; S, 6.0%); v_(max)(KBr) 3446, 2929, 2855, 1653, 1589, 1461, 1289, 1139, 1088, 914, 831,692, 588 cm⁻¹. TGA analysis show decomposition begins around ˜200° C.(FIG. 1). The surface area as well as pore size diameter and total porevolume were determined to be 0.7426 m² g⁻¹, 162.6 nm, 0.030 cm³ g⁻¹,respectively. Scheme 1 is presented below.

BSDF Characterizations

FT-IR spectra were recorded before and after adsorption on a PerkinElmer 16F FTIR spectrometer in a region of 4000-400 cm⁻¹ (FIG. 2). FIG.2 is a FT-IR spectra for: (a) BSDF, (b) BSDF loaded with lead ions.Thermal analysis was conducted to determine the stability and modes ofdecomposition of BSDF terpolymer. SEM-EDX images show the surfacemorphology and the existence of lead ions (Pb²⁺) before and after theadsorption process on the synthesized terpolymer.

Adsorption Experiments

Adsorption set of experiments were conducted using the technique ofbatch equilibrium in polyethylene vials (50 ml capacity). The pH of thesolutions was adjusted by adding 0.1M HNO₃ or NaOH. A mixture of 30 mgof BSDF immersed in an aqueous solution (20 ml) of Pb(NO₃)₂ with aconcentration of 5 mg L⁻¹ of Pb²⁺ ions was stirred at different timesand temperatures. Once the adsorption experiment was complete theterpolymer was filtered and the concentration of the metal ions in thefiltrate was analyzed. The adsorption capacity of BSDF was calculatedusing Eq. (1):

$\begin{matrix}{q_{{Pb}^{2 +}} = \frac{\left( {C_{o} - C_{e}} \right)V}{W}} & (1)\end{matrix}$where C_(o) is the initial metal ion concentration (mg L⁻¹), C_(e) isthe metal ion concentration at equilibrium (mg L⁻¹), Vis the volume ofsolution (L), W is the weight of BSDF terpolymer (g), and q_(Pb) ²⁺ isthe adsorption capacity at equilibrium (mg g⁻¹).Quality Control and Quality Assurance

Quality control (QC) was maintained beginning with the design of theexperimental work, sampling and continue through the final validation ofthe obtained results. QC for lead ion determinations included repeatedof injections and periodic analysis of standard solution. The loss oflead and contamination of aliquots were limited to a minimum as per therequirements of quality control and assurance of results. The relativestandard deviation of the results was ≦5%.

A terpolymer for the removal of toxic metal ions from aqueous solutionhas been synthesized by polycondensation of bisphenol-S,paraformaldehyde and 1,6-diaminohexane in DMF as solvent. Thepolycondensation reaction was fast and the product was produced within 3minutes at 60° C. as a light yellow resinous material that was left tocure at 80° C. for 24 h which indicates the potential importance forindustrial application. The structure was in agreement with theelemental analysis. FIG. 1 is a TGA analysis of BSDF. Thermal analysis(FIG. 1) showed initial decomposition around 180° C., and showed twosteps of decomposition: step 1; slow loss of 21.6% due to the loss ofSO₂, step 2; large major loss of 61.2% due to the combustion of thenitrogenated organic fraction with the release of CO₂, NO_(x) and H₂Ogases; the residual mass at 800° C. was found to be 18.0%.

Effect of pH on the Adsorption

The pH of the solution of the lead ions plays a critical role in theadsorption process. This parameter influences the lead chemistry inwater and metal binding sites (G. Raj, Chemical Kinetics in AdvancedPhysical Chemistry, 4th ed., Geol Publishing House: Meerut, India;(2001) 669-676—incorporated herein by reference in its entirety). As afunction of pH solution, at pH more than 7, the lead ions precipitateforming a lead hydroxide precipitate (P. X. Sheng, Y. P. Ting, J. P.Chen, L. Hong, Sorption of lead, copper, cadmium, zinc, and nickel bymarine algal biomass: characterization of biosorptive capacity andinvestigation of mechanisms, J. Colloid Interface Sci. 275 (2004)131-141—incorporated herein by reference in its entirety). Below pH ofaround 6, positive lead ions Pb(II) is the dominant species in thesolution. Between pH above 6 and around 8, lead undergoes hydrolysis toPb(OH)⁺ (H. B. Bradl, Adsorption of heavy metal ions on soils and soilsconstituents, J. Colloid Interface Sci. 277 (2004) 1-18; M. Machida, R.Yamazaki, M. Aikawa, H. Tatsumoto, Role of minerals in carbonaceousadsorbents for removal of Pb(II) ions from aqueous solution, Sep. Purif.Technol. 46 (2005) 88-94—each incorporated herein by reference in itsentirety). The effect of pH on the adsorption of lead ions on BSDF wasinvestigated using the synthetic solutions of lead with initialconcentrations of 5 ppm (FIG. 3). FIG. 3 is a graph that shows theeffect of pH on the adsorption capacity of Pb²⁺ ions by BSDF. Theobtained results of the conducted experiments indicate that lead ionsuptake by BSDF increased with the increase of pH from 3 to 7.Experiments beyond pH of 7 were not undertaken due to the formation oflead hydroxide precipitate. At pH of around 3, the ions uptake was lowdue to the increase in competition between protons (H⁺) from thesolution and positively charged metal ions. The highest efficiency ofBSDF was observed at pH between 5 and 6 with around 90% uptake of thelead ions after 30 min of contact time. Thus, the maximum uptake ofPb(II) on the surface of the BSDF was obtained at pH range between 5 and6.

Adsorption Properties of BSDF

The adsorption of metal ions on BSDF is due to the presence of chelatingfunctional ligands of —NH and —OH groups that are characterized in FIG.2A as a broad strong peak at 3446 cm⁻¹ due to the overlap of bothfunctional groups, which upon Pb²⁺adsorption shifted to 3427 cm⁻¹. Thiscould be related to the effect on the stretching vibrational as shown inFIG. 2b . The symmetric and asymmetric vibrations of S═O were assigned1139 and 1289 cm⁻¹. The C—N absorption frequency was assigned 1461 cm⁻¹that disappeared upon the appearance of a new strong peak at 1378 cm⁻¹which is assigned to the presence of the ionic nitrate group; asadsorption experiments were performed in lead nitrate solutions. Thisresult implies the potential use BSDF as an anion exchanger.

Adsorption Kinetics

Adsorption kinetics were performed as follow: 20 ml solution of 5 mg L⁻¹of Pb²⁺ ions with 30 mg of BSDF were stirred at 25° C., 35° C. and 50°C. for different times starting from 5 minutes to 3 hours, in order toinvestigate the rate and mechanism of adsorption. The adsorption processshown in FIG. 4 was found to be fast and efficient as the % removal ofPb²⁺ ions reached 100% within 3 hours at 25° C. and 50 minutes at 50° C.(FIG. 4, FIG. 5A) which indicates that higher temperatures increases theefficiency of adsorption by increasing the diffusion of Pb²⁺ into BSDF.FIG. 4 is a graph of the percent removal of Pb²⁺ ions by BSDF atdifferent temperatures. FIG. 5A is a graph of the effect of time on theadsortption of Pb²⁺ by BSDF at different temperatures. FIG. 5B is agraph of Lagergren-second order kinetics of Pb²⁺ adsorption on BSDF atdifferent temperatures. FIG. 5C is a graph of activation energydetermination for Pb²⁺ adsorption on BSDF. FIG. 5D is a graph of anintraparticle diffusion plot for Pb²⁺ adsorption on BSDF at differenttemperatures. Lagergren first-order and second-order kinetic models wereemployed, and Intraparticle diffusion model was used to investigate themechanism of adsorption.

Lagergren First-order Kinetic Model

Lagergren kinetic models were used to investigate the rate and mechanismof the adsorption process, first order kinetic model is based on theassumption that each lead ion is adsorbed to one site on the adsorbentsurface. The following equation is used in the linear form ofLagergren-first order kinetic model:

$\begin{matrix}{{\log\left( {q_{e} - q_{t}} \right)} = {{\log\mspace{14mu} q_{e}} - \frac{k_{1}t}{2.303}}} & (1)\end{matrix}$where q_(e) and q_(t) (mg g⁻¹) are the adsorption capacities atequilibrium and at time t (h), respectively, and k₁ is the rate constantfor the first order adsorption process (h⁻¹). k₁ and q_(e,cal), atdifferent temperatures were experimentally determined and calculateusing the intercept ad slope of equation 1 (Table 2). The poorregression values and experimental data showed the inadequacy of usingthe first-order kinetic model. These results suggest that the adsorptionof Pb²⁺ on BSDF did not follow the first-order kinetic model (Y. S. Ho,Citation review of lagergren kinetic rate equation on adsorptionreactions, Scientometrics, 59 (2004) 171-177; H. K. Boparai, D. M.O'Carroll, Kinetics and thermodynamics of cadmium ion removal byadsorption onto nanozerovalent iron particles, J. Hazard. Mater. 186(2011) 458-465—each incorporated herein by reference in its entirety).Table 2 is presented below.

TABLE 2 Lagergren First and Second-Order Kinetic Model fittingParameters for the adsorption of Pb²⁺ ions^(a) on BSDF Lagergrenfirst-order Lagergren second-order Metal Temp q_(e,exp) k₁ q_(e,cal) k₂h^(b) q_(e,cal) E_(a) ion (K) (mg g⁻¹) (h⁻¹) (mg g⁻¹) R² (h⁻¹g mg⁻¹)(h⁻¹g⁻¹ mg) (mg g⁻¹) R² (kJ mol⁻¹) Pb²⁺ 298 2.857 1.98 2.04 0.8962 0.2791.90 2.61 0.9964 4.51 308 2.857 0.48 1.20 0.7158 0.305 2.55 2.89 0.9980323 2.857 0.13 0.705 0.2813 0.330 3.33 3.17 0.9951 ^(a)Initial metal ionconcentration 1 mg/L. ^(b)Initial adsorption rate h = k₂ q_(e) ².Lagergren Second-order Kinetic Model

Lagergren second-order kinetic model is used to analyze the kinetics ofchemical adsorption from liquid to solid adsorbent. The linear form ofLagergren second-order can be described as (FIG. 5B):

$\begin{matrix}{\frac{t}{q_{t}} = {\frac{1}{k_{2}q_{e}^{2}} + {\frac{1}{q_{e}}t}}} & (2)\end{matrix}$where q_(e) and q_(t) (mg g⁻¹) are the adsorption capacities atequilibrium and at time t (h), respectively, and k₂ is the rate constantfor the second-order adsorption process (g mg⁻¹h⁻¹), and k₂q_(e) ² (mgg⁻¹h⁻¹) or h is the initial adsorption rate.

The experimental data with high regression values fits Lagergrensecond-order kinetic model which assumes chemical adsorption whichagrees with BET analysis. The low surface area of BSDF concludes thatthe adsorption process depends mainly on chemisorption rather thanphysisorption. The increase in temperature shows increase in theadsorption capacity which may be due to higher accessibility of Pb²⁺ions toward the adsorption sites in BSDF.

The adsorption activation energy (FIG. 5C) can be determined using therate constants (k₂) from the second-order kinetic model and temperatureby Arrhenius linear equation described as:

$\begin{matrix}{{lnk}_{2} = {\frac{E_{a}}{2.303\mspace{14mu}{RT}} + {constant}}} & (3)\end{matrix}$where k₂ is the second-order rate constant (g mg⁻¹h⁻¹), E_(a) isactivation energy of the adsorption process (kJ mol⁻¹), T is theabsolute temperature (° K) and R is the universal gas constant (8.314 Jmol⁻¹ K). The low activation energy for the adsorption process (4.51kJmol⁻¹) indicates the favorability of the chemisorption process.Intraparticle Diffusion Model

The mechanism of adsorption for a solid-liquid adsorption process can bedescribed by three steps: the transfer of metal ions from the bulksolution through liquid film to the adsorbent external surface (filmdiffusion), intraparticle diffusion, where the metal ions diffusethrough the external surface into the pores of the adsorbent, andadsorption on the interior surface of the adsorbent.

The final step is considered rapid and is negligible as the adsorptionprocess comes to equilibrium. To identify the mechanism controlling theadsorption mechanism, Weber and Morris Intraparticle diffusion model wasused in order to determine whether the rate-limiting step is controlledby film diffusion or Intraparticle diffusion and can be described usingthe following equation:q _(t) =K _(i) t ^(0.5) +x _(i)   (4)where q_(t) is the adsorption capacity at time t, K_(i) is the rateconstant of intraparticle diffusion, x_(i) is related to boundary layerthickness. In order for the adsorption process to be totally controlledby Intraparticle diffusion model a plot of q_(t) versus t^(0.5) has tofit the model and pass through the origin. But it has been reported thatthe plot of q_(t) versus t^(0.5) is multilinear and the adsorptionprocess proceeds via multiple steps (E. I. Unuabonah, K. O. Adebowale,B. I. Olu-Owaolabi, kinetic and thermodynamic studies of the adsorptionof lead (II) ions onto phosphate-modified kaolinite clay, J. Hazard.Mater. 144 (2007) 386-395—incorporated herein by reference in itsentirety).

The adsorption process of Pb²⁺ ions by BSDF (FIG. 5D) showed threelinear steps: first, rapid adsorption that represents film diffusion,the second linear step shows gradual increase in the adsorption capacityrepresenting the rate-limiting step by Intraparticle diffusion (table3), and finally, the third linear step which is considered reachingequilibrium. Table 3 is presented below.

TABLE 3 Intraparticle Diffusion parameters for the adsorption of Pb²⁺ions on BSDF at different temperatures. Temp K_(i) Intercept valuesMetal ion (K) (mg g⁻¹ h^(0.5)) (x_(i)) R_(i) R² Pb²⁺ 298 1.144 1.3920.513 0.9768 308 1.328 1.425 0.501 0.9943 323 1.458 1.477 0.483 0.9583

As shown in FIG. 5D the plot did not pass through the origin indicatingthat Intraparticle diffusion is not the only rate determining step. Asshown in table 3 the intercept values increased as the temperatureincreased which could be attributed to the increase in thickness of theboundary layer surrounding the adsorbent, suggesting that film diffusionbecomes more effective in the rate determining step with the increase intemperature (F. C. Wu, R. L. Tseng. R. S. Juang, initial behavior ofIntraparticle diffusion model used in the description of adsorptionkinetics, Chem. Eng. J. 153 (2009) 1-8; T. I. Kamins, polycrystallinesilicon for integrated circuits and displays, Kluwer AcademicPublishers, Norwell, Mass., 1998—each incorporated herein by referencein its entirety).

In order to study the initial behavior of adsorption, the initialadsorption factor of the Intraparticle diffusion model (R_(i)) can bedescribed as:

$\begin{matrix}{R_{i} = {1 - \frac{x_{i}}{q_{e}}}} & (5)\end{matrix}$where x_(i) is the initial adsorption amount and q_(e) the finaladsorption amount at the longer time. As shown in table 3, R_(i) valuesdecrease with the increase in temperature which can be explained by theincrease role of film diffusion in the rate determining step. The Rivalues were found to be ˜0.5 indicating strong initial adsorption of˜50% and the rest is governed by Intraparticle diffusion.SEM-EDX Analysis of BSDF and BSDF Loaded with Pb²⁺ Ions

Loaded and unloaded BSDF terpolymers were studied by scanning electronmicroscopy (SEM). BSDF terpolymer was soaked in a 20 mg L⁻¹ solution oflead nitrate (Pb(NO₃)₂) for 3 hours, filtered and washed with distilledwater then dried under vacuum at 60° C. until constant weight isachieved. The loaded and unloaded BSDF polymers were coated with a 5 nmthin film of gold. The SEM-EDX analysis (FIG. 6) proved the compositionof BSDF terpolymer, and also, proved the capability of BSDF to adsorblead ions. The color of BSDF (light yellow) changed after adsorption oflead ions into white which also shows the capability to adsorb lead ionsform aqueous solutions. FIG. 6A is a SEM image and EDX analysis forBSDF. FIG. 6B is a SEM image and EDX analysis for BSDF loaded with leadions.

In order to assess the potential of the BSDF for the treatment ofwastewater in real life, wastewater samples, were collected from thefield, and then treated with BSDF. Some wastewater samples were alsospiked with 1 mg L⁻¹ or with 5 mg L⁻¹ of lead. Then, 20 mL of eachsample was loaded with 30 mg of BSDF under the optimized conditions. Theresults presented in table 4 indicate the high efficiency and capabilityof BSDF to adsorb toxic metals like arsenic, cadmium and lead. Thehigher capability of BSDF in eliminating toxic metal ions fromwastewater can be assigned to the increase in the —HN: moiety over the—H₂N⁺ moiety in the chain structure as discussed in the characterizationsection. Table 4 is presented below.

TABLE 4 Comparison of metals concentration from water treatment plantsample (Dhahran, Saudi Arabia) before and after adding the treatmentwith BSDF. After treatment (μg L⁻¹) Original sample Original samplespiked with Pb²⁺ ions Metal (μg L⁻¹) 0 1000 (μg L⁻¹) 5000 (μg L⁻¹) Pb0.826 ± 0.018 <MDL 0.427 4.24 Co 0.360 ± 0.09  <MDL <MDL <MDL Cu 29.36 ±0.064  3.80 1.84  3.19 Zn 395.4 ± 0.025  0.218 0.241 1.22 As  6.34 ±0.024 <MDL <MDL <MDL Mo 14.63 ± 0.018 12.64 10.72  10.67  Cd  0.58 ±0.015 <MDL <MDL  0.058 Sb <0.012 <MDL <MDL <MDL Mean and standarddeviation of three replicates (n = 3). ±Values are the method detectionlimit (MDL), 3σ of the blank sample.

A novel cross-linked terpolymer (BSDF) composed of Bisphenol-S,formaldehyde and 1,6-diaminohexane was synthesized and characterized.The efficiency of BSDF as adsorbent was tested for the adsorption oflead ions from aqueous solutions under various operational variables,such as contact time, pH and temperature. The results showed that thelead ions uptake by was rapid. It was also found that the removalpercentage was high in pH range between 5 and around 6. The adsorptionof lead ions increased with increasing temperature, indicating that theadsorption process is endothermic in nature. The novel terpolymer wasfound to have excellent % removal that reached 100% in the removal oflead ions. The novel terpolymer showed high efficiency in the removal oftoxic metal ions which implies the high potential for industrialapplications.

A cross-linked terpolymer (BSDF) has been synthesized bypolycondensation of Bisphenol-S, Formaldehyde and 1,6-Diaminohexane. Theterpolymer was found to be highly efficient in eliminating lead ionsfrom aqueous solutions. The adsorption of lead ions on BSDF was studiedunder different conditions such as: pH, contact time and temperature.The adsorption kinetics fits Lagergren second order kinetic model thatcame in agreement with the low surface area as a chemisorption process.The adsorption of lead ions reached 100% removal efficiency of lead ionsat 5 mg L⁻¹ concentration at pH=5.5. The low activation energy of 4.5kJ/mol for the adsorption of lead ions on BSDF supported the spontaneousand fast adsorption of lead ions on BSDF. Applying BSDF on non-spikedand spiked real wastewater samples under optimum conditions revealed thehigh efficiency of BSDF in removing toxic metal ions. Accordingly, theuse of BSDF can be considered a promising method for eliminating leadions from wastewater effectively.

Thus, the foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. As will be understood by thoseskilled in the art, the present invention may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting of the scopeof the invention, as well as other claims. The disclosure, including anyreadily discernible variants of the teachings herein, define, in part,the scope of the foregoing claim terminology such that no inventivesubject matter is dedicated to the public.

The invention claimed is:
 1. A cross-linked terpolymer having a formula(I):

wherein: n is the number of repeating units and n is an integer fromgreater than 1 to 1,000.
 2. The cross-linked terpolymer of claim 1,which is in the form of a solid material having a surface area in therange of 0.720-0.750 m²g⁻¹.
 3. The cross-linked terpolymer of claim 1,which is in the form of a solid material having a pore size diameter inthe range of 161.0-163.0 nm.
 4. The cross-linked terpolymer of claim 1,which is in the form of a solid material having a total pore volume inthe range of 0.028-0.032 cm³g⁻¹.
 5. A method of making the cross-linkedterpolymer of claim 1, the method comprising: polycondensingbisphenol-S, formaldehyde and 1,6 diaminohexane in the presence of asolvent comprising dimethylformamide at a temperature of 70-90° C. for22-26 hours to form the cross-linked terpolymer.
 6. A method forremoving metal ions from an aqueous solution, the method comprising:contacting an aqueous solution comprising metal ions with an adsorbentcomprising the cross-linked terpolymer of claim
 1. 7. The method ofclaim 6, wherein after contacting, one or more metal ions arecoordinated to one or more nitrogen atoms of the cross-linkedterpolymer.
 8. The method of claim 6, wherein the metal ions are leadions.
 9. The method of claim 6, wherein the contacting removes at least90% of the lead ions from the aqueous solution.
 10. The method of claim8, wherein the activation energy for the adsorption of lead ions ontothe adsorbent is in the range of 4.0-5.0 kJ/mol.
 11. The method of claim6, wherein the aqueous solution has a pH in the range of 5-6.
 12. Thecross-linked terpolymer of claim 1, wherein n is an integer from 100 to1,000.
 13. The cross-linked terpolymer of claim 1, which has a weightaverage molecular weight of 1,500-350,000 g/mol.